Repeated Sprint Ability: Energy Systems during repeated high intensity workouts

[FOCUS]

In recent years, a large number of industry debates have focused on which methods should be employed while training repeated-sprint athletes. Some propose the concept of sport-specificity, utilizing only techniques that mirror the on-field movement demands of the athlete, while others rely on more generic, interval-based training to develop the energy systems. In the 2011 review Repeated-Sprint Ability – Part II: Recommendations for Training, Bishop et al. aim to assess the validity of these methods and others in hopes to form a consensus on the most effective protocol.

Energy Systems 101
While an expansive discussion about the energy systems exceeds the intent of this review, I think it’s important to cover the basics in terms of how these systems interact with one another. For the sake of terminology, I’ll define the energy systems in the following manner:

■Alactic (ATP-CP) – immediate energy
■Lactic (Glycolytic) – intermediate energy
■Aerobic – long-term energy
My initial education on the energy systems came in the following format – the first 30 seconds of activity is predominantly alactic, the next minute and a half is all glycolysis, and it’s not until the 2 minute mark that the aerobic systems begins to contribute significantly towards energy production. As it turns out, this approach to metabolism is shortsighted in light of more current research.



These energy systems, while often taught in a successive fashion, all turn on at the exact same time – right at the onset of activity. And they will work as hard as they possibly can to meet the metabolic demands present.

For example, during a 100-meter sprint, the aerobic system is cranking through substrates as fast as possible, doing its best to contribute to energy production. It’s the short nature of the race, not the aerobic system’s inactivity, which limits the total amount of ATPs produced aerobically.

It’s also important to note that at about the 60-70s mark of activity, aerobic metabolism becomes the dominant source of energy production. And with repeated bouts of activity (e.g., interval training), you become more and more aerobic with each successive bout. If the aerobic component of an athlete’s energy production is lacking, they will fatigue faster when required to produce repeated, high-intensity bouts of activity.

Each energy system has both a power and a capacity component. The power of an energy system is defined by the rate at which that system can turn on and begin producing ATPs. The capacity, on the other hand, is the duration at which an energy system can maintain energy production at a certain work level.

Both of these components will come into play when assigning the training methods for repeated-sprint athletes.

What is a Repeated-Sprint Athlete?
The authors of the review define two basic parameters for a repeated-sprint athlete:

■Short-duration, high-intensity activity of ≤ 10 seconds
■Brief recovery periods of ≤ 60 seconds
To excel in their sports, these athletes are required to not only produce a great deal of power, but also do so repeatedly while maintaining a low fatigue index (i.e., the performance decrement from the first sprint to the last). A high power output is critical to our definition – a marathon runner who

[FOCUS]

maintains a very low fatigue index during repeated bouts of activity but lacks appreciable power output would not be classified as a good repeated-sprint athlete.

In general, if an athlete plays a team sport on a large field, he or she can be classified as a repeated-sprint athlete. Non-field athletes met with similar metabolic demands during competition could also fall into this category. Examples include sports like rugby, soccer, American football, and mixed martial arts.

Given the nature of these athletes’ movement demands, achieving full recovery during their sport is not an option, thus declines in performance are inevitable. In a 1993 study by Gaitainos, subjects performing 10 maximal effort sprints on a 6-seconds on, 30-seconds off cadence incurred a 27% drop in power output from the first sprint to the last (870W – 635W).

To put these results into perspective, imagine the ramifications for American football players. By the 10th play of a drive, athletes on both sides of the ball are functioning at an average capacity 27% lower than when the drive started. In this example, the limitations of an athlete’s energy systems can stand as the determinant to whether his team finishes a drive or not.

Energy Demands of Repeated-Sprint AthletesFor the most part, the energy systems demands of a repeated-sprint athlete are alactic-aerobic. The alactic system is responsible for providing the immediate energy to drive high-intensity movement while the aerobic system serves as the foundation for substrate recovery between bouts of activity.

Despite it’s frenetic pace when viewed on television, soccer provides a great example for this energy systems trade-off. A 2009 time-motion study by Osgnach et al. examined the metabolic workload of over 400 elite-level soccer players. They concluded that more than 70% of the total match duration was performed at low “aerobic” intensities, while only 1-3% of the match was performed high-intensities (“sprinting”). The overall work to rest ratio of these soccer players averaged out to a 2-4 second sprint every 90 seconds.

Time-motion research for other field sports yields similar observations. In both rugby (pictured below) and Irish hurling, on average, the total “sprint” time is only about 5% of the match. Just as in soccer, the bulk of the metabolic demand (70-80%) is low to medium-intensity.





Simply following the ball (or discounting the huddle, in the case of American football) might mislead onlookers into overestimating the glycolytic demands of repeated-sprint sports. However, in light of the Osgnach study and time-motion research on other sports, it’s clear that the bulk of the metabolic demands lie in the other two energy systems.

This begs the question – why, if these athletes rely so heavily on the alactic and aerobic systems, is there still overwhelming support of high-intensity, glycolytic-based training methods?

One theory is that high-intensity seems to be the rule in training. The current American system thrives on running people into the ground – it’s primarily the athletes possessing genetic superiority that rise to the top levels of competition and get to play. While I’m not advocating an easy way out, research points to much smarter methods in preparing our athletes for sport.

Overreliance on high-intensity techniques can produce undesirable ramifications for repeated-sprint athletes. For example, the constant sympathetic nervous system activation associated with this style of training can impair an athlete’s recovery between bouts of activity and between individual training sessions.

And due to the competing adaptations present, a focus on glycolytic development ensures suboptimal aerobic development. Considering the aforementioned ATP-CP and medium-intensity demands of repeated-sprint athletes, inadequate preparation will lead them to dip into glycolysis sooner and cause them to fatigue faster.

The Biochemistry of Interval Training
While time-motion studies can give us a pretty clear picture into the metabolic demands of a given sport, it’s also important to dig into the research and assess what’s going on at the cellular level.

The following image, taken from an excellent 1999 study by Parolin et al., provides an accurate presentation of what interval training actually looks like to our energy systems.



The subjects of this study were asked to produce three 30-second bouts of sprinting (cycling) followed by four-minute recovery periods. The A graph above provides a histogram of the first sprint while B illustrates the third.

What’s most striking in this data is the apparent disappearance of the lactic component from the first sprint to the third, even with the significant rest period between bouts. While the first six seconds of the sprint place a huge demand on the alactic system in both trials, notice how the aerobic component in B is required to contribute much sooner (and more significantly) than in A. This increased aerobic demand is created by the fact that, due to an accumulation of its own by-products, lactic metabolism ends up inhibiting itself.

So, what happens if an athlete doesn’t have adequate aerobic capacity to “fill in” for lactic metabolism and is faced with repeated bouts of high-intensity activity? The only option is to reduce his or her power output.

Anyone with a background in track can most likely attest to this metabolic phenomenon – it’s like running repeat 400-meter sprints when you’ve got nothing left after the first one. Slowing down is really the only option to finish the workout.

In another study that more closely mimics the demands of repeated-sprint athletes, researchers asked subjects to perform 10 six-second intervals on a 30-second recovery period. The results are pictured below with the first sprint on the left and the tenth on the right:



During the first sprint, the demand is close to even between the two anaerobic systems – roughly 55% alactic and 45% lactic. By the tenth “play”, the alactic system is responsible for greater than 80% of the anaerobic energy production, most of that coming from creatine phosphate (PCr). How, then, is all this new PCr generated?

The answer is aerobically – we’re actually using the aerobic system to regenerate substrates to fuel alactic metabolism.

[FOCUS]

PCr-O2 StudyCurrent research suggests that aerobic metabolism contributes 13% of the energy towards a 10-second sprint and up to 27% in a 20-second sprint. This fact, coupled with the studies above, provides substantial support for the indispensability of aerobic development in repeated-sprint athletes.

Training the Limiting Factors
In almost all cases, effective programming comes down to minimizing an athlete’s limitations while maximizing his or her strengths – energy systems development is no different.

The authors of the review highlight three specific areas of potential limitation in repeated-sprint athletes:

1.Energy Supply
2.H+ Accumulation
3.Muscle Activation
Energy Supply

Phosphocreatine Resynthesis

A six-second, all-out sprint has been shown to reduce intramuscular PCr content up to 55%. Given the metabolic demands of repeated-sprints, only partial restoration of PCr stores between bouts of activity is to be expected.

Theoretically, the better an athlete can resynthesize PCr the better they can reproduce sprint performance, thus, training the pathways that augment this resynthesis mechanism could be critical to increasing performance in repeated-sprint athletes.

As I cited earlier, aerobic metabolism is essential for PCr resynthesis during the recovery period between bouts of high-intensity exercise. In his book Adaptation in Sports Training, Viru proposes increased creatine kinase isoenzyme content/activity as the biological mechanism behind this phenomenon.

The authors cite a study by Bishop D. et al. with the following training guidelines:

■2 minutes at 100% VO2max
■1 minute recovery period
■6-12 sets per session
■3 times per week for 5 weeks
This protocol, specifically augmenting aerobic power, was shown to significantly improve PCr resynthesis during the first 60 seconds following high-intensity exercise and also improved intramuscular H+ buffering capacity.

Studies implementing more traditional interval-training protocols (e.g., 30-seconds on, 90-240-seconds off) failed to produce any change in the rate of PCr resynthesis. The authors attribute inadequate improvement in aerobic fitness as the culprit.

In conclusion, aerobic development is critical for alactic substrate recovery.

Lactic Metabolism

While the research presented above certainly minimizes the importance of the lactic system relative to our other two energy systems, we do need it for optimal repeat-sprint performance (though its effects are the most pronounced during the initial sprint).

To best maximize performance, we need to choose training methods that best augment the most important enzymes for lactic metabolism – namely, phoshofructokinase (PFK) and phosphorylase.

Relative to traditional interval training methods (e.g., 30-seconds on, 90-240-seconds off), which show no positive enzymatic adaptation, studies show the greatest increases in PFK and phosphorylase activity with the following protocol:

■20-30 seconds maximal intensity
■Light activity/Active rest between sets
■Rest periods ~10 minutes (yields larger peak lactate compared to 4 minute rest periods)
■2-4 sets x 1-3 reps/set
■Twice per week
As lactic adaptations tend to level off in about four to six weeks, the bulk of the training year should be spent developing the other two systems. With that said, increasing lactic power through the training methods described above can lead to significant increases repeat-sprint performance and should absolutely be utilized when appropriate.

Aerobic Metabolism

The authors cite the following aerobic adaptations as beneficial to the repeat-sprint athlete:

■Improved ATP/PCr resynthesis
■Greater mitochondrial respiratory capacity
■Faster O2 uptake kinetics
■Accelerated post-sprint muscle re-oxygenation rate
■Higher anaerobic threshold
■Higher VO2max
Essentially, increasing the aerobic contribution to repeated bouts of activity will result in a lower fatigue index, thus higher levels of performance throughout the duration of competition.

The authors highlight aerobic power intervals, like those outlined in the above discussion on PCr resynthesis, as an effective way to achieve the necessary aerobic adaptations to excel in repeat-sprint sports. I’d like to provide two more methods taken from Joel Jamieson’s Ultimate MMA Conditioning that can further augment aerobic development in repeat-sprint athletes.

Cardiac Output Development:

■20-60 minutes of activity (LSD, mobility circuits, skill-practice, etc.)

[FOCUS]

■Heart rate in the 120-150bpm range
■Once or twice a week, as needed
Cardiac output development is important in creating a strong aerobic foundation as well as generating whole body aerobic power. Aim for a resting heart rate of ≤ 60 beats per minute as a marker for adequate adaptation in repeat-sprint sports.

Threshold Training:

■10-20 minutes +/- 5bpm of anaerobic threshold
■5-10 minutes rest between sets
■1-5 reps (fewer reps at longer durations)
■One to three times per week
If we can raise an athlete’s anaerobic threshold, we extend the amount of energy they can produce at high-intensities before dipping into lactic metabolism, at which point fatigue will accumulate at a much higher rate. As a means for threshold training, sprints, circuits, or skill-practice can be utilized.

H+ Accumulation

As highlighted through multiple studies cited in the review, both muscle buffer capacity and changes in muscle/blood pH are correlated with the performance decrement in repeated sprints. The authors suggest that training methods targeting the increased removal of H+ from the muscle could serve as a means to increase repeat-sprint performance.

At the cellular level, this requires the augmentation of both buffering substrates and the intramuscular content of monocarboxylate transporters (MCTs).

Though more research in this area must be pursued for a definitive protocol in optimizing H+ buffering/transport, aerobic power intervals (described above) seem to yield the greatest benefit in both increased buffering capacity and MCT content.

Muscle Activation

One cannot discount the considerable neural component to sprinting.

As fatigue accumulates across repeated bouts of sprinting, studies have shown subjects to incur decreased ability in fully activate the involved musculature. Though the authors do not present a comprehensive case in this regard towards training repeated-sprint athletes, it’s conceivable that any training that augments muscle activation could be of benefit – plyometrics, strength training, etc.

The authors propose that increasing muscle activation would have its most pronounced benefits on initial sprint performance, while the aforementioned methods would be more important in reducing fatigue across multiple bouts of activity.

Training Strategies for Repeated-Sprint Athletes

The authors conclude the review by presenting the following recommendations towards programming for repeated sprint athletes:

1. Prioritize both alactic and aerobic development – the former to increase performance and the latter to reduce the performance decrement.
We’ve already seen how vital the aerobic system can be for the repeated-sprint athlete. Whether it’s substrate regeneration between bouts or increased vagal tone/recovery between sessions, optimal aerobic development should really stand as a cornerstone in a repeated-sprint athlete’s programming arsenal. Not yet discussed, though, is the importance of the alactic system development.

Drawing a comparison to mixed-martial arts, the alactic system provides a fighter’s knockout power. For our repeated-sprint athlete, they need well-developed alactic power and capacity to produce high-intensity movement immediately and for the necessary duration before shifting back into a predominantly aerobic, recovery mode.

The guidelines for developing both alactic power and capacity are as follows:

Alactic Power Intervals

■7-10 seconds per rep
■Heart rate-based active recovery to 120bpm (ensures maximal effort)
■5-6 reps per set
■1-2 sets per session
■One to three times per week
Alactic Capacity Intervals

■10-15 seconds per rep
■20-90 seconds active rest (set for sport-specificity)
■10-12 reps per set
■2-3 sets per session
■One to three times per week
As far as means go, sprints, jumps, and max-effort sport-specific drills are recommended.

2. Though research has not yet investigated this topic, including traditional sprint training might be beneficial to repeat-sprint athletes.

Research has linked improved single-sprint performance to increased mean repeated-sprint time across successive bouts, so it’s plausible that this finding could have ramifications for repeated-sprint athletes.

The methods recommended include traditional strength/power training, alactic power and capacity development, as well as lactic power development.

3. Utilize Block Periodization with high-level athletes to maximize adaptation.

While beginners present with a large window of adaptation and concurrent training may be acceptable, advanced athletes should not be handled in a similar manner.

[FOCUS]

Between the increased concentration of loading and conflicting stimuli for differing physiological systems, it’s paramount to periodize these athletes’ programming effectively. Both Vladimir Issurin’s Block Periodization and Joel Jamieson’s Ultimate MMA Conditioning provide an excellent framework for doing so.

Conclusion
Repeated-sprint athletes require a unique blend of explosive power and aerobic capacity to excel in competition.

While this review is by no means exhaustive, I hope it’s provided some insight to the energy systems demands of these athletes, as well as some practical training methods in addressing their metabolic needs.


Repeat Sprint Ability – Part II25
Share

[FOCUS]

van 8weeksout van Joel Jameson

[FOCUS]

en dit roep ik eigenlijk al jaren mensen, traine je aerobe en je anaerobe alactische systeem
en imho hoort dit er bij: het trainen van het lactische systeem (in de verzuring) moet af toe getraind worden, maar slechts ten hoogste 1 keer per twee weken